Viscous Hydrocarbon Treatment Method by In-situ Asphaltene Inerting

ABSTRACT

The invention concerns a method for treating viscous hydrocarbon containing asphaltenes, which consists in performing the following steps: precipitating at least part of the asphaltenes by adding into the hydrocarbon an appropriate solvent; adding into the hydrocarbon polymerization products adapted to encapsulate the precipitated asphaltenes to inert same.

FIELD OF THE INVENTION

The present invention relates to the field of production and transportation of viscous effluents, notably crude oils referred to as heavy crudes, for example because of their asphaltene content.

BACKGROUND OF THE INVENTION

Known viscous crude transportation methods consist in thinning down the crude by heating, mixing with a thinning product or by treatment prior to transportation, for example by passing into aqueous emulsion. However, these techniques are energy-costly or they implement complex processes requiring considerable infrastructures that penalize reservoir development.

In the present description, what is referred to as slurry is a suspension or a dispersion of solid particles in a liquid that can be circulated, notably by pumping. This type of slurry flow is already commonly used during estuary or river dredging operations, and in the mining industry. The advantage is to allow transportation of a maximum amount of solid cuttings with as little pumping energy as possible. Concerning the petroleum industry, slurry transportation is used to enrich fuels in coal particles and thus to increase their heating value. The solid content can reach 60% by mass while keeping acceptable flow properties.

The present invention preferably applies to heavy crudes. It also applies to extra-heavy crudes, bitumen, bituminous sand or equivalent. It thus consists in modifying the structural organization of the heavy crude which behaves like a viscous colloidal suspension, to obtain a particle suspension of lower viscosity. The particles concerned by this change are, within the scope of a preferred embodiment of the present invention, asphaltenes. Asphaltenes are the molecules of highest molecular weight contained in certain crudes. They are characterized by their high polarity and by the presence of polycondensed aromatic rings. Overlap of these particles spread in the crude is greatly responsible for the high viscosity of heavy crudes. This overlap can be eliminated by maintaining the asphaltenes in form of encapsulated solid particles in the crude. This configuration change can be reached by combining, in the crude, precipitation and inerting of the asphaltenes, then by dispersing the encapsulated asphaltenes in the base liquid, notably under strong mechanical stirring. A non limitative method of operation has been developed and it has been checked that the resulting morphology change of the crude in suspension form indeed leads to a viscosity decrease.

Advantageously, according to the invention, the asphaltene particles are transported in solid form by the crude base liquid in which these asphaltenes are dispersed so that the liquid obtained is more fluid than the original crude. Thus, transportation by pumping in pipes is facilitated up to refining plants. In these refining plants, the slurry is fed either as it is into these treating plants, or after a stage of separation of the suspended solid particles, the asphaltenes, which may simplify downstream processes.

SUMMARY OF THE INVENTION

The present invention thus relates to a method of treating a viscous asphaltene-containing hydrocarbon, wherein the following stages are carried out:

precipitating at least part of the asphaltenes by adding a suitable solvent to the hydrocarbon,

adding to the hydrocarbon polymerization products suited to encapsulate the precipitated asphaltenes so as to inert them.

According to the method, the asphaltenes can be precipitated with n-alkane.

Polymerization products can be added to form a membrane around asphaltene particles by interfacial polycondensation.

Di or triamine, or a mixture thereof, and an acyl dichloride can be added to form an aromatic polyamide at the surface of the asphaltene particles so as to form a membrane.

Alkyd resins suited to cross-link at the surface of the asphaltene particles can be added.

A siccative can be added as an agent favouring cross-linking.

The invention also relates to the application of the method intended to obtain a decrease in the viscosity of a viscous asphaltene-containing hydrocarbon.

The method can apply to pipe transportation of a viscous asphaltene-containing hydrocarbon.

BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the present invention will be clear from reading the description hereafter of embodiments given by way of non limitative example, with reference to the accompanying figures wherein:

FIG. 1 shows the results of an embodiment according to the invention, and

FIG. 2 shows the performance with time of the method according to the invention.

DETAILED DESCRIPTION

According to the invention, at least two polymerization modes for encapsulating asphaltenes contained in a viscous hydrocarbon so as to inert them can be described.

The invention shows how encapsulation of the asphaltenes within a heavy crude allows to durably decrease the viscosity of such oils.

The invention is not limited to these two encapsulation modes.

The first embodiment of the invention is a polymerization that consists in an interfacial polycondensation. The goal is to achieve a polymer material synthesis at the solid-liquid interface between the asphaltenes and their environment. This method is based on the selection of two appropriate monomers, one soluble in the liquid phase and the other having great affinities with asphaltenes. It can be noted that the polymer obtained forms a membrane around the asphaltenes and should not be soluble in the liquid phase. The protocol of the preferred operating method uses synthesis of aromatic polyamides obtained from the reaction between a di or triamine and an acyl dichloride. Because of its high polarity, the di or triamine is preferably located at the surface of the asphaltenes. On the other hand, acyl dichloride is soluble in the medium surrounding the asphaltenes. The polyamide obtained is insoluble in the liquid phase and it foul's at the surface of the asphaltene particles. It belongs to the polyaramids family whose aromatic structure is known to provide them with temperature resistance, high mechanical properties and good solvent and oxidizing agent resistance [Odian: “Principles of Polymerization”, 3^(rd) Ed., John Wiley & Sons, Inc., 1994].

The operating method developed allows to modify the structural organization of the heavy crude by changing it into a suspension of non colloidal encapsulated particles of greatly and durably reduced viscosity. This protocol is carried out in situ; it requires no prior crude deasphalting with asphaltene extraction, treatment and reincorporation. The encapsulation method described simply requires prior addition of an n-alkane in controlled proportion in order to precipitate the asphaltenes. The encapsulation reaction is then directly carried out on the encapsulated asphaltenes without requiring filtering, then dispersing them. Once the polymer membrane formed, the n-alkane is evaporated, possibly to be recycled. Besides, part of the alkane can be left in place. A light petroleum cut can also be added to adjust the viscosity value.

Operating Method Example

The n-alkane selected is added in the desired proportion to the crude. After 20-minute mechanical stirring during which the asphaltenes precipitate, the di or triamine is introduced in the selected proportion by mass in relation to the amount of asphaltenes. Tributylamine is also added. Its purpose is to neutralize the hydrochloric acid released during the reaction between an amine group and an acyl chloride function. The mixture is stirred for one hour during which the di or triamine adds on to the precipitated asphaltene particles. The acyl dichloride is then introduced in the selected proportion by mole in relation to the di or triamine. Encapsulation then takes place by synthesis of the polyamide between the di or triamine and the acyl dichloride at the surface of the asphaltenes. The reaction is initiated by slight heating between 30° C. and 35° C., which is maintained under reflux for one hour. The n-alkane is then evaporated. A suspension of granulous aspect is obtained, the size of the particles reaching several hundred microns.

Test 1: Influence of the Proportion of N-Alkane Added

Three samples were prepared for encapsulation of the asphaltenes of a heavy crude containg 17% by mass thereof. The monomers selected to produce the interfacial polycondensation reaction are melamine (supplied by Sigma-Aldrich for example) and sebacoyl dichloride (supplied by VWR). The triamine is introduced in a proportion of 5% by mass of the asphaltenes. The proportion of acyl dichloride is set at 1.7 mole to 1 mole of melamine. The n-alkane selected for precipitating the asphaltene particles is pentane. Its proportion is known to influence both the size of the particles and the precipitation efficiency. This parameter is varied between 10, 15 and 20 ml/g crude. In each case, after the interfacial polycondensation reaction and pentane evaporation, the samples are observed by optical microscopy and their viscosity is measured by means of a controlled-stress rheometer. In this example, the size of the capsules changes with the proportion of pentane, ranging respectively, for the samples prepared with 10, 15 and 20 ml/g crude respectively, between 300, 700 and 50 μm.

FIG. 1 gives the viscosity V of the samples (in Pa·s) as a function of the proportion of pentane added Q (in ml/g). The results show that the encapsulated samples are less viscous than the original heavy crude and that there is an optimum n-alkane content for better reducing the viscosity. This optimum content (here between 10 and 15 ml/g) has to be calibrated according to the nature of the heavy crude, i.e. the state of solvation and of concentration of its asphaltenes.

Test 2: Influence of the Proportion of Monomers on the Viscosity Decrease of the Encapsulated Samples

In order to observe the influence of the proportion of monomers on the quality of the encapsulated products, four samples were prepared from 2.5, 5, 10 and 20% by mass of melamine in relation to the asphaltenes. The proportion of sebacoyl dichloride is still set at 1.7 mole per mole of melamine introduced. The tests use pentane as the n-alkane with a content of 15 ml/g crude. In each case, after interfacial polycondensation reaction and pentane evaporation, the samples are observed by optical microscopy and their viscosity is measured by means of a controlled-stress rheometer. The optical microscopy images allow to visualize the excess polymer formed with the high monomer concentrations, a polymer whose presence in excess causes a high viscosity. Table 1 shows that the viscosity increases with the proportion of monomers. To observe the temperature resistance of these samples, the microscopic analyses are resumed after heating them to 80° C. for 1 hour. The total results show that a 5% melamine content is preferred to obtain a good compromise between the viscosity level and the temperature resistance.

TABLE 1 Viscosity at 20° C. of the samples encapsulated by interfacial polycondensation with various monomer proportions 2.5% 5% 10% 20% monomers monomers monomers monomers Viscosity 35 Pa · s 45 Pa · s 100 Pa · s 150 Pa · s

Test 3: Resistance with Time of the Samples Encapsulated by Interfacial Polycondensation

In order to check the resistance with time of crudes containing asphaltenes encapsulated by interfacial polycondensation, the viscosity of a sample was measured at different time intervals. The sample used is the one prepared from 5% mass melamine, 1.7 mole/mole of sebacoyl dichloride, precipitation of the asphaltenes being obtained with pentane introduced in a proportion of 15 ml/g crude. The rheological measurements are shown in FIG. 2, which gives the viscosity V (in Pa·s) as a function of the shear rate t (s⁻¹). Curve 1 represents the crude, curve 2 after encapsulation, curve 3 40 days later, and curve 4 66 days later. The curves show the stability of the product with time.

The second method proposed for encapsulating the asphaltenes of a crude consists in causing cross-linking of alkyd resins at the surface thereof. Alkyd resins are unsaturated polyesters (presence of double bonds) obtained from polyol and natural fatty acids. They are characterized by their vegetable oil content, referred to as oil length, which provides them with a siccative power, i.e. a capacity to polymerize in the presence of oxygen. This cross-linking process involves several physico-chemical mechanisms according to whether the doubles bonds are simple or conjugated [Marshall et al., Polymer, 28, 1093, 1987], [Solomon, “The chemistry of organic film formers”, Wiley-Intersciences, New York, 1967].

It can include addition of a siccative whose purpose is to accelerate cross-linking by favouring oxygen supply. The siccatives used are in most cases metallic oxides. As for the first polymerization mode by interfacial polycondensation described above, the operating method developed for this second mode allows to modify the structural organization of the heavy crude by changing it into a suspension of encapsulated particles of greatly and durably reduced viscosity. This protocol is carried out in situ ; it requires no prior deasphalting of the crude with extraction, treatment and reincorporation of the asphaltenes. The encapsulation method described simply requires prior addition of an n-alkane in controlled proportion in order to precipitate the asphaltenes. The alkyd resins are preferably located at the surface of the asphaltenes. The cross-linking reaction then takes place directly on the precipitated asphaltenes. Once the membrane formed, the n-alkane is evaporated, possibly to be recycled. Besides, part of the alkane can be left in place. A light petroleum cut or a solvent can also be added to adjust the viscosity value.

Operating Method Example

The n-alkane selected is added in the desired proportion to the crude. After 15-minute mechanical stirring during which the asphaltenes precipitate, the alkyd resins, the possible siccative and a dispersant are introduced. Mechanical stirring is maintained under heating at 35° C. for two hours. The n-alkane is finally evaporated. A smooth suspension is obtained.

Test 4: Influence of the Proportion of Alkyd Resins on the Viscosity Decrease

In order to observe the influence of the proportion of alkyd resins on the quality of the encapsulated products, three samples were prepared from 4.6 and 8% by mass of Synolac 6883 (supplied by the DSM Company) in relation to the asphaltenes. The proportion of siccative (Combi QS from the Nuodex Company) is set at 4% by mass in relation to the resin and the proportion of dispersant (Montane 80 from the Seppic Company) is 1% by mass of the alkane added. The tests are carried out using pentane as the n-alkane in a proportion of 10 mug crude. In each case, after cross-linking reaction and evaporation, the viscosity of the samples is measured by means of a controlled-stress rheometer. The results of Table 2 show that the lowest viscosity level is obtained for a 6% resin content.

TABLE 2 Viscosity at 20° C. of the samples encapsulated by cross-linked alkyd resins 4% 6% 8% monomers monomers monomers Viscosity 75 Pa · s 50 Pa · s 70 Pa · s

Test 5: Temperature Resistance of the Cross-Linked Samples

In order to check the temperature resistance of the cross-linked products, the viscosity of a sample was measured after heating at 50° C. and 80° C. for 1 hour. The sample used was the one prepared from 6% by mass of alkyd resins Synolac 6883 (see test 4). The rheological measurements are given in Table 3 and show a good product stability. Despite the intensive thermal treatment, notably at 80° C., the viscosity of the crude is not affected.

TABLE 3 Temperature resistance of the samples encapsulated by cross-linked alkyd resins, viscosity measured at 20° C. Without thermal After 1 h After 1 h treatment at 50° C. at 80° C. Test with siccative 50 Pa · s 60 Pa · s 80 Pa · s

Test 6: Influence of the Siccative

In order to observe the influence of the added siccative, a sample was prepared with 6% Synolac resins without adding any siccative. Its viscosity was measured after preparation and after heating at 50° C. and 80° C. for 1 hour. The results show that the sample without siccative has the same viscosity as the equivalent sample with siccative (50 Pa·s). On the other hand, the sample without siccative is much less resistant to the intensive thermal treatment performed at 80° C. (see Table 4).

TABLE 4 Temperature resistance of the samples encapsulated by cross-linked alkyd resins, influence of the siccative, viscosity measured at 20° C. Without thermal After 1 h After 1 h treatment at 50° C. at 80° C. Test without siccative 50 Pa · s 60 Pa · s 180 Pa · s 

1) A method of treating a viscous asphaltene-containing hydrocarbon, wherein the following stages are carried out: precipitating at least part of the asphaltenes by adding a suitable solvent to the hydrocarbon, adding to the hydrocarbon polymerization products suited to encapsulate the precipitated asphaltenes so as to inert them. 2) A method as claimed in claim 1, wherein the asphaltenes are precipitated with n-alkane. 3) A method as claimed in claim 1, wherein polymerization products are added to form a membrane around the asphaltene particles by interfacial polycondensation. 4) A method as claimed in claim 3, wherein di or triamine, or a mixture thereof, and an acyl dichloride are added to form an aromatic polyamide at the surface of the asphaltene particles. 5) A method as claimed in claim 1, wherein alkyd resins suited to cross-link at the surface of the asphaltene particles are added. 6) A method as claimed in claim 5, wherein a siccative acting as an agent favouring cross-linking is added. 7) Application of the method as claimed in claim 1 to obtain a decrease in the viscosity of a viscous asphaltene-containing hydrocarbon. 8) Application of the method as claimed in claim 7 for pipe transportation of a viscous asphaltene-containing hydrocarbon. 9) A method as claimed in claim 2, wherein polymerization products are added to form a membrane around the asphaltene particles by interfacial polycondensation. 10) A method as claimed in claim 9, wherein di or triamine, or a mixture thereof, and an acyl dichloride are added to form an aromatic polyamide at the surface of the asphaltene particles. 11) A method as claimed in claim 2, wherein alkyd resins suited to cross-link at the surface of the asphaltene particles are added. 12) A method as claimed in claim 11, wherein a siccative acting as an agent favouring cross-linking is added. 